Variable magnification optical system and imaging apparatus

ABSTRACT

A variable magnification optical system consists of, in order from an object side, a first optical system remaining stationary during changing magnification and a second optical system including a plurality of lens groups moving during changing magnification. The first optical system includes a first mirror and a second mirror having reflective surfaces arranged to face each other. The first mirror has a reflective surface concave toward the object side. The second mirror has a reflective surface convex toward the image side. An intermediate image is formed between the second mirror and the second optical system. Predetermined conditional expressions relating to the partial dispersion ratios of the lenses included in the second optical system are satisfied.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority under 35 U.S.C. § 119 to Japanese Patent Application No. 2018-033717, filed on Feb. 27, 2018 and Japanese Patent Application No. 2018-243491, filed on Dec. 26, 2018, the contents of which are hereby expressly incorporated herein by reference in their entirety.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to a variable magnification optical system and an imaging apparatus.

2. Description of the Related Art

In the related art, variable magnification optical systems comprising catadioptric systems have been proposed. For example, variable magnification optical systems each including two mirrors and a plurality of lenses are described in JP1999-202208A (JP-H11-202208A), U.S. Pat. Nos. 4,235,508A, 4,971,428A, and CN106772963A.

SUMMARY OF THE INVENTION

In recent years, the demand for surveillance cameras used for remote monitoring at harbors and/or airports and the like has increased. Accordingly, the demand for variable magnification optical systems of the telephoto system and the super telephoto system usable for such surveillance cameras has increased. In such a variable magnification optical system, it is desired that fluctuations in spherical aberration, astigmatism, distortion, and chromatic aberration during changing magnification are small while achieving a high variable magnification ratio, and favorable imaging performance is provided.

However, the variable magnification optical system described in JP1999-202208A (JP-H11-202208A) has large fluctuations in astigmatism and distortion during changing magnification. The variable magnification optical system described in U.S. Pat. No. 4,235,508A has a low variable magnification ratio. The variable magnification optical system described in U.S. Pat. No. 4,971,428A has large distortion. In the variable magnification optical system described in CN106772963A, spherical aberration is not satisfactorily corrected.

In view of the above situations, the present invention has an object to provide a variable magnification optical system, which has small fluctuations in various aberrations during changing magnification and has favorable optical performance while achieving a high variable magnification ratio, and an imaging apparatus comprising the variable magnification optical system.

In order to solve the above problem, the variable magnification optical system according to an embodiment of the present invention consists of, in order from an object side: a first optical system that includes two reflecting mirrors having reflective surfaces arranged to face each other and remains stationary with respect to an image plane during changing magnification; and a second optical system that includes at least two positive lenses and at least one negative lens. The two reflecting mirrors consist of a first reflecting mirror that has a reflective surface concave toward the object side and reflects light, which is originated from an object, toward the object side, and a second reflecting mirror that has a reflective surface convex toward an image side and reflects the reflected light, which is reflected from the first reflecting mirror, toward the image side. The second optical system includes, successively in order from a position closest to the object side, a first lens group that consistently moves to the object side during changing magnification from a wide-angle end to a telephoto end and has a positive refractive power, and a second lens group that moves in a direction of an optical axis with a locus different from a locus of the first lens group during changing magnification and has a positive refractive power. An intermediate image is formed between the second reflecting mirror and the first lens group, and the intermediate image is re-formed through the second optical system. In addition, assuming that an average value of partial dispersion ratios of all the positive lenses in the second optical system between a g line and an F line is θgFp, and an average value of partial dispersion ratios of all the negative lenses in the second optical system between the g line and the F line is θgFn, it is preferable to satisfy Conditional Expression (1). −0.04<θgFp−θgFn<0.1  (1)

In the variable magnification optical system of the present invention, it is preferable to satisfy Conditional Expression (1-1). −0.02<θgFp−θgFn<0.06  (1-1)

In the variable magnification optical system of the present invention, assuming that an average value of Abbe numbers of all the positive lenses in the second optical system at a d line is νdp and an average value of Abbe numbers of all the negative lenses in the second optical system at the d line is νdn, it is preferable to satisfy Conditional Expression (2), and it is more preferable to satisfy Conditional Expression (2-1). 10<νdp−νdn<40  (2) 14<νdp−νdn<35  (2-1)

In the variable magnification optical system of the present invention, assuming that an average value of partial dispersion ratios of all the positive lenses in the second optical system between a C line and a t line is θCtp and an average value of the partial dispersion ratios of all the negative lenses in the second optical system between the C line and the t line is θCtn, it is preferable to satisfy Conditional Expression (3), and it is more preferable to satisfy Conditional Expression (3-1). −0.1<θCtp−θCtn<0.1  (3) −0.07<θCtp−θCtn<0.05  (3-1)

In the variable magnification optical system of the present invention, it is preferable that the first optical system includes a field lens group that consists of two or less lenses and that has a positive refractive power and that is a lens component closest to the intermediate image.

In the variable magnification optical system of the present invention, it is preferable that the first reflecting mirror is an optical element having a power at a position closest to the object side on an optical path.

In the variable magnification optical system according to the present invention, it is preferable that the first optical system includes a correction lens group consisting of two or less lenses which are disposed in an optical path from the first reflecting mirror to the second reflecting mirror and in an optical path from the second reflecting mirror to a position of the intermediate image and which have a common optical axis with respect to the first reflecting mirror and the second reflecting mirror.

In the variable magnification optical system of the present invention, assuming that an average value of the partial dispersion ratios of all the negative lenses in the second optical system between a C line and a t line is θCtn, it is preferable to satisfy Conditional Expression (4), and it is more preferable to satisfy Conditional Expression (4-1). 0.75<θCtn<0.9  (4) 0.77<θCtn<0.85  (4-1)

In the variable magnification optical system of the present invention, assuming that an average value of the partial dispersion ratios of all the positive lenses in the second optical system between the C line and the t line is θCtp, it is preferable to satisfy Conditional Expression (5), and it is more preferable to satisfy Conditional Expression (5-1). 0.75<θCtp<0.9  (5) 0.78<θCtp<0.85  (5-1)

In the variable magnification optical system of the present invention, assuming that an average value of Abbe numbers of all the negative lenses in the second optical system at a d line is νdn, it is preferable to satisfy Conditional Expression (6). 50<νdn<65  (6)

In the variable magnification optical system of the present invention, assuming that an average value of refractive indices of all the negative lenses in the second optical system at a d line is Ndn, it is preferable to satisfy Conditional Expression (7). 1.5<Ndn<1.75  (7)

In the variable magnification optical system of the present invention, assuming that an average value of partial dispersion ratios of all the negative lenses in the second optical system between the g line and the F line is θgFn, it is preferable to satisfy Conditional Expression (8). 0.53<θgFn<0.58  (8)

In the variable magnification optical system of the present invention, assuming that an average value of partial dispersion ratios of all the positive lenses in the second optical system between a g line and an F line is θgFp, it is preferable to satisfy Conditional Expression (9). 0.5<θgFp<0.65  (9)

In the variable magnification optical system of the present invention, assuming that an average value of Abbe numbers of all the positive lenses in the second optical system at a d line is νdp, it is preferable to satisfy Conditional Expression (10). 70<νdp<100  (10)

In the variable magnification optical system of the present invention, assuming that an average value of refractive indices of all the positive lenses in the second optical system at a d line is Ndp, it is preferable to satisfy Conditional Expression (11). 1.43<Ndp<1.75  (11)

An imaging apparatus of the present invention comprises the variable magnification optical system of the present invention.

In the present specification, it should be noted that the terms “consisting of ˜” and “consists of ˜” mean that the lens may include not only the above-mentioned elements but also lenses substantially having no refractive powers, optical elements, which are not lenses, such as a stop, a filter, and a cover glass, and mechanism parts such as a lens flange, a lens barrel, an imaging element, and a camera shaking correction mechanism.

In the present specification, it should be noted that the “˜ group having a positive refractive power” means that the group has a positive refractive power as a whole. Likewise, the “˜ group having a negative refractive power” means that the group has a negative refractive power as a whole. “A lens having a positive refractive power”, “a lens having a positive power”, and “a positive lens” are synonymous. “A lens having a negative refractive power”, “a lens having a negative power”, and “a negative lens” are synonymous. The “lens group” is not limited to a configuration using a plurality of lenses, but may consist of only one lens. The “single lens” means one uncemented lens. However, a compound aspheric lens (a lens which is integrally composed of a spherical lens and a film having an aspheric shape formed on the spherical lens, and functions as one aspheric lens as a whole) is not be considered as a cemented lens, and is treated as a single lens. The “lens component” means a lens of which air contact surfaces are two surfaces including an object side surface and an image side surface on the optical axis, and one lens component means one single lens or a group of cemented lenses. The “having a power” means that a reciprocal of the focal length is not zero. The signs of the refractive powers, the surface shapes, and the radii of curvature of the surfaces of an optical element including an aspheric surface are assumed as those in the paraxial region unless otherwise specified. The sign of the radius of curvature of the surface convex toward the object side is positive and the sign of the radius of curvature of the surface convex toward the image side is negative. The “focal length” used in a conditional expression is a paraxial focal length. The values of conditional expressions other than conditional expressions relating to the partial dispersion ratio are values in the case of using the d line as a reference in a state where the object at infinity is in focus.

The “d line”, “C line”, “F line”, “g line”, and “t line” described in this specification are emissions lines. In the present specification, it is assumed that the wavelength of d line is 587.56 nm (nanometers), the wavelength of C line is 656.27 nm (nanometers), the wavelength of F line is 486.13 nm (nanometers), the wavelength of g line is 435.84 nm (nanometers), and the wavelength oft line is 1013.98 nm (nanometers).

The partial dispersion ratio θgF between the g line and the F line of a certain lens is defined by θgF=(Ng−NF)/(NF−NC), where Ng, NF, and NC are the refractive indices of the lens at the g line, the F line, and the C line. The partial dispersion ratio θCt between the C line and the t line of a certain lens is defined by θCt=(NC−Nt)/(NF−NC), where Nt, NF, and NC are the refractive indices of the lens at the t line, the F line, and the C line.

According to the present invention, it is possible to provide a variable magnification optical system, which has small fluctuations in various aberrations during changing magnification and has favorable optical performance while achieving a high variable magnification ratio, and an imaging apparatus comprising the variable magnification optical system.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view illustrating a configuration and an optical path of a variable magnification optical system (variable magnification optical system of Example 1 of the present invention) according to an embodiment of the present invention at a wide-angle end and a telephoto end.

FIG. 2 is a cross-sectional view illustrating a configuration and an optical path of a variable magnification optical system at the wide-angle end and the telephoto end according to Example 2 of the present invention.

FIG. 3 is a cross-sectional view illustrating a configuration and an optical path of a variable magnification optical system at the wide-angle end and the telephoto end according to Example 3 of the present invention.

FIG. 4 is a cross-sectional view illustrating a configuration and an optical path of a variable magnification optical system at the wide-angle end and the telephoto end according to Example 4 of the present invention.

FIG. 5 is a cross-sectional view illustrating a configuration and an optical path of a variable magnification optical system at the wide-angle end and the telephoto end according to Example 5 of the present invention.

FIG. 6 is a cross-sectional view illustrating a configuration and an optical path of a variable magnification optical system at the wide-angle end and the telephoto end according to Example 6 of the present invention.

FIG. 7 is a cross-sectional view illustrating a configuration and an optical path of a variable magnification optical system at the wide-angle end and the telephoto end according to Example 7 of the present invention.

FIG. 8 is a cross-sectional view illustrating a configuration and an optical path of a variable magnification optical system at the wide-angle end and the telephoto end according to Example 8 of the present invention.

FIG. 9 is a cross-sectional view illustrating a configuration and an optical path of a variable magnification optical system at the wide-angle end and the telephoto end according to Example 9 of the present invention.

FIG. 10 is a cross-sectional view illustrating a configuration and an optical path of a variable magnification optical system at the wide-angle end and the telephoto end according to Example 10 of the present invention.

FIG. 11 is a diagram of aberrations of the variable magnification optical system according to Example 1 of the present invention.

FIG. 12 is a diagram of aberrations of the variable magnification optical system according to Example 2 of the present invention.

FIG. 13 is a diagram of aberrations of the variable magnification optical system according to Example 3 of the present invention.

FIG. 14 is a diagram of aberrations of the variable magnification optical system according to Example 4 of the present invention.

FIG. 15 is a diagram of aberrations of the variable magnification optical system according to Example 5 of the present invention.

FIG. 16 is a diagram of aberrations of the variable magnification optical system according to Example 6 of the present invention.

FIG. 17 is a diagram of aberrations of the variable magnification optical system according to Example 7 of the present invention.

FIG. 18 is a diagram of aberrations of the variable magnification optical system according to Example 8 of the present invention.

FIG. 19 is a diagram of aberrations of the variable magnification optical system according to Example 9 of the present invention.

FIG. 20 is a diagram of aberrations of the variable magnification optical system according to Example 10 of the present invention.

FIG. 21 is a schematic configuration diagram of an imaging apparatus according to an embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a cross-sectional view illustrating a configuration and an optical path of a variable magnification optical system according to an embodiment of the present invention. In FIG. 1, aberrations at the wide-angle end state are shown in the upper part indicated by “WIDE”, and aberrations at the telephoto end state are shown in the lower part indicated by “TELE”. The example shown in FIG. 1 corresponds to the variable magnification optical system of Example 1 to be described later. FIG. 1 shows a state where the object at infinity is in focus, where the left side of the drawing is the object side and the right side of the drawing is the image side.

The variable magnification optical system according to the present embodiment consists of, in order from the object side to the image side, a first optical system U1 and a second optical system U2. The first optical system U1 remains stationary with respect to an image plane Sim during changing magnification. The second optical system U2 includes at least two positive lenses and at least one negative lens.

The first optical system U1 includes two reflecting mirrors having reflective surfaces arranged to face each other. According to this configuration, it is possible to shorten the total length by folding the optical path. The two reflecting mirrors consist of a first reflecting mirror and a second reflecting mirror. The first mirror M1 of the present embodiment corresponds to the first reflecting mirror, and the second mirror M2 corresponds to the second reflecting mirror.

It is preferable that the first mirror M1 is an optical element having a power at a position closest to the object side in the optical path. In a case where a dioptric system is disposed to be closer to the object side than the first mirror M1 in the optical path, the dioptric system requires a large aperture, which is expensive. Further, in a case where the dioptric system is disposed to be closer to the object side than the first mirror M1 in the optical path, the center of gravity of the variable magnification optical system is biased toward the tip portion, and the weight balance thereof is deteriorated. Thus, this configuration is not preferable. Furthermore, since light does not pass through a reflective optical element, there is also an advantage that the degree of freedom of selection of a material is higher than that of a transmissive optical element.

The first mirror M1 has a reflective surface concave toward the object side and is configured to reflect light, which is originated from the object, toward the object side. The second mirror M2 has a reflective surface convex toward the image side and is configured to reflect the reflected light, which is reflected from the first mirror M1, toward the image side. With such a configuration, it is possible to shorten the total length without generating chromatic aberration, and thus the optical system becomes suitable for a super telephoto system. As an example, FIG. 1 shows an example in which the first mirror M1 and the second mirror M2 are configured to have a common optical axis Z.

The reflective surface of the first mirror M1 and the reflective surface of the second mirror M2 are preferably spherical. In such a case, the optical system can be manufactured inexpensively, and it is possible to reduce deterioration in image quality caused by eccentricity and/or collapse.

The second optical system U2 includes, in order from a position closest to the object side, a first lens group G1 that consistently moves to the object side during changing magnification from a wide-angle end to a telephoto end and has a positive refractive power, and a second lens group G2 that moves in a direction of an optical axis with a locus different from a locus of the first lens group G1 during changing magnification and has a positive refractive power. In other words, the first lens group G1 is disposed to be closest to the object side in the second optical system U2, and the second lens group G2 is disposed adjacent to the first lens group G1 on the image side in the first lens group G1. The plurality of lens groups having positive refractive powers are continuously arranged in the second optical system U2 which is a variable magnification optical system. Thereby, it is possible to suppress occurrence of spherical aberration on the wide-angle side, fluctuation in spherical aberration during changing magnification, fluctuation in astigmatism during changing magnification, and fluctuation in distortion during changing magnification. As, a result, a high variable magnification ratio can be easily achieved. In addition, it is possible to reduce the effective diameter of the lens group that moves during changing magnification.

An intermediate image is formed between the second mirror M2 and the first lens group G1. FIG. 1 shows a position P of the intermediate image in the optical axis. The intermediate image is re-formed on the image plane Sim through the second optical system U2. That is, the second optical system U2 functions as a relay optical system. By using the variable magnification optical system as a reimaging optical system, it is possible to reduce the diameter of the lens group moving during changing magnification, and it is possible to achieve reduction in weight and an increase in speed of the changing magnification operation.

The first optical system U1 may be configured to include a field lens group Gfd which is a lens component closest to the intermediate image. It should be noted that the “intermediate image” in the term “closest to the intermediate image” described herein is an intermediate image during focusing on the object at infinity. Further, the “field lens group Gfd closest to the intermediate image” also includes a case where the position P of the intermediate image is located inside the field lens group Gfd. It is preferable that the field lens group Gfd is a lens group that consists of two or less lenses and has a positive refractive power. By providing a positive refractive power in the vicinity of the intermediate image, it is possible to make the light of the peripheral angle of view intersect with the optical axis Z inside the variable magnification optical system. Thus, it is possible to suppress an increase in the effective diameter of the variable magnification optical system. For example, the field lens group Gfd in the example of FIG. 1 consists of a set of cemented lenses formed by cementing a lens Lf1 having a negative power and a lens Lf2 having a positive power in order from the object side. The lens Lf1 is concave toward the object side, the lens Lf2 is convex toward the image side, and the cemented surface between the lens Lf1 and the lens Lf2 is convex toward the object side.

In addition, the first optical system U1 may be configured to include the correction lens group Gc having the effect of aberration correction. The correction lens group Gc preferably consists of two or less lenses having the common optical axis Z with respect to the first mirror M1 and the second mirror M2. By setting the number to two or less, the load on the object side portion of the variable magnification optical system can be minimized. As a result, the solidity required for the mount for installing the variable magnification optical system can be reduced. In order to reduce the number of optical elements to be used and to improve manufacturability, it is preferable that the correction lens group Gc consists of one lens. The correction lens group Gc in the example of FIG. 1 consists of only one lens Lc1. For example, the lens Lc1 in FIG. 1 is a meniscus lens convex toward the object side. It should be noted that the correction lens group Gc may consist of two lenses, and in such a case, astigmatism can be satisfactorily corrected. For example, the correction lens group Gc may consist of two single lenses having a meniscus shape convex toward the object side.

It is preferable that the correction lens group Gc be disposed both in the optical path from the first mirror M1 to the second mirror M2 and in the optical path from the second mirror M2 to the position P of the intermediate image. That is, it is preferable to adopt a configuration in which the light passes the correction lens group Gc twice in a case where the light reflected by the first mirror M1 is directed toward the second mirror M2 and in a case where the light reflected by the second mirror M2 is directed to the position P of the intermediate image. As described above, the correction lens group Gc is disposed in the optical path in which the light reciprocates. Thereby, even in a case where the number of optical elements such as lenses and mirrors is reduced, it becomes easy to satisfactorily correct spherical aberration. In addition, even in a case where the number of optical elements is reduced and both the first mirror M1 and the second mirror M2 do not use an aspheric surface, it becomes easy to satisfactorily correct spherical aberration.

It is preferable that only the first mirror M1, the second mirror M2, the field lens group Gfd, and the correction lens group Gc are optical elements having powers included in the first optical system U1. Deterioration in the transmittance of the entire first optical system U1 can be suppressed by reducing the number of optical elements.

In the example of FIG. 1, the first optical system U1 has only a first mirror M1, a second mirror M2, a field lens group Gfd, and a correction lens group Gc as optical elements having powers. In the example of FIG. 1, all the optical elements of the first optical system U1 have a common optical axis Z. Regarding arrangement in which the optical path is not considered, the second mirror M2 is located closest to the object side, the correction lens group Gc is disposed near the image side of the second mirror M2, the first mirror M1 is disposed closer to the image side than the correction lens group Gc, and the field lens group Gfd is disposed near the first mirror M1. In the example of FIG. 1, the first mirror M1 has an annular shape of which the center is hollow. The intermediate image is located near the object side of the field lens group Gfd.

In the example of FIG. 1, light incident into the first optical system U1 along the optical path from the object side to the image side is first reflected by the first mirror M1, travels toward the object side, and is transmitted through the correction lens group Gc. Then, the light is reflected by the second mirror M2, travels toward the image side, is transmitted through the correction lens group Gc again, is transmitted through the field lens group Gfd, and is incident into the second optical system U2.

The second optical system U2 in the example of FIG. 1 consists of, in order from the object side to the image side along the optical axis Z, a first lens group G1, a second lens group G2, a third lens group G3, and a fourth lens group G4. In the example of FIG. 1, the first lens group G1 consists of three lenses L11 to L13, the second lens group G2 consists of one lens L21, the third lens group G3 consists of four lenses L31 to L34, and the fourth lens group G4 consists of one lens L41. However, the configuration shown in FIG. 1 is just an example. The variable magnification optical system may be configured such that the number of lens groups composing the second optical system U2 and the number of lenses composing each lens group are different from those in the example of FIG. 1.

In the example of FIG. 1, during changing magnification, the first lens group G1, the second lens group G2, and the third lens group G3 move by changing the distances between adjacent lens groups in the direction of the optical axis, and the fourth lens group G4 remains stationary with respect to the image plane Sim. That is, during changing magnification, the first lens group G1, the second lens group G2, and the third lens group G3 move in the direction of the optical axis with loci different from one another. In FIG. 1, during changing magnification from the wide-angle end to the telephoto end, the movement locus trG1 of the first lens group G1, the movement locus trG2 of the second lens group G2, the movement locus trG3 of the third lens group G3, and the movement locus trG4 of the fourth lens group G4 are schematically indicated by arrows between the wide-angle end state and the telephoto end state. The movement locus of the lens group that does not move during changing magnification as in the fourth lens group G4 is indicated by a straight arrow in the vertical direction.

It is preferable that the lens closest to the object side in the first lens group has a negative refractive power and is concave toward the object side. In such a case, the angle of the principal light of the off-axis light with respect to the optical axis Z can be reduced. As a result, it is possible to reduce fluctuations in the effective diameters of the lenses included in the first lens group G1 and the second lens group G2 during changing magnification.

It is preferable that the lens closest to the image side in the first lens group G1 and the lens closest to the object side in the second lens group G2 have positive refractive powers and are convex toward each other. In such a case, fluctuation in spherical aberration during changing magnification can be suppressed.

It is preferable that the second optical system U2 includes at least one lens group at the position closer to the image side than the second lens group G2, and the lens group closest to the image side in the second optical system U2 has a positive refractive power. In such a case, there is an advantage in correction of lateral chromatic aberration. The lens group closest to the image side in the second optical system U2 may be composed of one single lens. In such a case, it is possible to ensure the amounts of movement of the first lens group G1 and the second lens group G2. As a result, there is an advantage in achieving a high variable magnification ratio while suppressing fluctuations in various aberrations.

For example, as in the example shown in FIG. 1, the second optical system U2 consists of, in order from the object side, a first lens group G1 having a positive refractive power, a second lens group G2 having a positive refractive power, a third lens group G3 having a negative refractive power, and a fourth lens group G4 having a positive refractive power. During changing magnification, the first lens group G1, the second lens group G2, the third lens group G3 move in the direction of the optical axis with loci different from one another, and the fourth lens group G4 remains stationary with respect to the image plane Sim. In such a case, fluctuation in astigmatism during changing magnification can be suppressed.

Alternatively, as in Example 7 described later, the second optical system U2 may consist of, in order from the object side, a first lens group G1 having a positive refractive power, a second lens group G2 having a positive refractive power, and a third lens group G3 having a positive refractive power. During changing magnification, the first lens group G1 and the second lens group G2 may move in the direction of the optical axis with loci different from one another, and the third lens group G3 may remain stationary with respect to the image plane Sim. In such a case, since all the lens groups composing the second optical system U2 have positive refractive powers, it is possible to suppress deterioration in image quality caused by eccentricity and/or collapse of the lens groups while suppressing fluctuation in spherical aberration during changing magnification.

Alternatively, as in Example 9 to be described later, the second optical system U2 may consist of, in order from the object side, a first lens group G1 having a positive refractive power, a second lens group G2 having a positive refractive power, and a third lens group G3 having a positive refractive power. During changing magnification, the first lens group G1, the second lens group G2, and the third lens group G3 may move in the direction of the optical axis with loci different from one another. In such a case, all the lens groups composing the second optical system U2 have positive refractive powers, and the degree of freedom of the paraxial solution increases. Thus, it is possible to suppress deterioration in image quality caused by eccentricity and/or collapse of lens groups while suppressing fluctuation in spherical aberration during changing magnification and fluctuation in astigmatism during changing magnification.

Alternatively, as in Example 10 described later, the second optical system U2 may consist of, in order from the object side, a first lens group G1 having a positive refractive power and a second lens group G2 having a positive refractive power. The first lens group G1 and the second lens group G2 may move in the direction of the optical axis with loci different from one another during changing magnification. In such a case, since the configuration is simple, the changing magnification mechanism can be simplified.

Regarding focusing, for example, it is possible to perform focusing by changing a distance between the first mirror M1 and the second mirror M2. In that case, it is preferable to adopt any one of the following methods: a method of performing focusing by moving only the first mirror M1 in the direction of the optical axis with respect to the image plane Sim; a method of performing focusing by moving only the second mirror M2 in the direction of the optical axis with respect to the image plane Sim; and a method of performing focusing by integrally moving the second mirror M2 and the correction lens group Gc in the direction of the optical axis. Alternatively, focusing may be performed by moving a part of the lens groups of the second optical system U2 in the direction of the optical axis.

Next, a configuration relating to conditional expressions of the variable magnification optical system of the present embodiment will be described. Assuming that an average value of the partial dispersion ratios of all the positive lenses in the second optical system U2 between the g line and the F line is θgFp and an average value of the partial dispersion ratio of all the negative lenses in the second optical system U2 between the g line and the F line is θgFn, it is preferable that the variable magnification optical system of the present embodiment satisfies Conditional Expression (1). By satisfying Conditional Expression (1), occurrence of secondary longitudinal chromatic aberration and secondary lateral chromatic aberration in the visible light region can be suppressed. In addition, in a case of a configuration in which Conditional Expression (1-1) is satisfied, it is possible to obtain more favorable characteristics. In a case of a configuration in which Conditional Expression (1-2) is satisfied, it is possible to obtain further more favorable characteristics. −0.04<θgFp−θgFn<0.1  (1) −0.02<θgFp−θgFn<0.06  (1-1) −0.015<θgFp−θgFn<0  (1-2)

Assuming that an average value of the Abbe numbers of all the positive lenses in the second optical system U2 at the d line is νdp and an average value of the Abbe numbers of all the negative lenses in the second optical system U2 at the d line is νdn, it is preferable to satisfy Conditional Expression (2). By not allowing the result of Conditional Expression (2) to be equal to or less than the lower limit, correction of longitudinal chromatic aberration becomes easy. By not allowing the result of Conditional Expression (2) to be equal to or greater than the upper limit, occurrence of secondary chromatic aberration can be suppressed. In addition, in a case of a configuration in which Conditional Expression (2-1) is satisfied, it is possible to obtain more favorable characteristics. 10<νdp−νdn<40  (2) 14<νdp−νdn<35  (2-1)

Assuming that an average value of the partial dispersion ratios of all the positive lenses in the second optical system U2 between the C line and the t line is θCtp and an average value of the partial dispersion ratio of all the negative lenses in the second optical system U2 between the C line and the t line is θCtn, it is preferable to satisfy Conditional Expression (3). By satisfying Conditional Expression (3), occurrence of secondary chromatic aberration in the wavelength range from red to infrared can be suppressed. In addition, in a case of a configuration in which Conditional Expression (3-1) is satisfied, it is possible to obtain more favorable characteristics. In a case of a configuration in which Conditional Expression (3-2) is satisfied, it is possible to obtain further more favorable characteristics. −0.1<θCtp−θCtn<0.1  (3) −0.07<θCtp−θCtn<0.05  (3-1) −0.06<θCtp−θCtn<0.015  (3-2)

Assuming that an average value of the partial dispersion ratios of all the negative lenses in the second optical system U2 between the C line and the t line is θCtn, it is preferable to satisfy Conditional Expression (4). By not allowing the result of Conditional Expression (4) to be equal to or less than the lower limit, it becomes easy to ensure a difference in Abbe number between the negative lens and the positive lens, and it becomes easy to correct the primary chromatic aberration. By not allowing the result of Conditional Expression (4) to be equal to or greater than the upper limit, it becomes easy to correct the secondary chromatic aberration in the wavelength range from red to infrared. In addition, in a case of a configuration in which Conditional Expression (4-1) is satisfied, it is possible to obtain more favorable characteristics. 0.75<θCtn<0.9  (4) 0.77<θCtn<0.85  (4-1)

Assuming that an average value of the partial dispersion ratios of all the positive lenses in the second optical system U2 between the C line and the t line is θCtp, it is preferable to satisfy Conditional Expression (5). By not allowing the result of Conditional Expression (5) to be equal to or less than the lower limit, it becomes easy to correct the secondary chromatic aberration in the wavelength range from red to infrared. By not allowing the result of Conditional Expression (5) to be equal to or greater than the upper limit, it becomes easy to ensure a difference in Abbe number between the negative lens and the positive lens, and it becomes easy to correct the primary chromatic aberration. In addition, in a case of a configuration in which Conditional Expression (5-1) is satisfied, it is possible to obtain more favorable characteristics. 0.75<θCtp<0.9  (5) 0.78<θCtp<0.85  (5-1)

Assuming that an average value of the Abbe numbers of all the negative lenses in the second optical system U2 at the d line is νdn, it is preferable to satisfy Conditional Expression (6). By not allowing the result of Conditional Expression (6) to be equal to or less than the lower limit, it becomes easy to select a material having a small partial dispersion ratio between the g line and the F line, and it becomes easy to correct the secondary chromatic aberration in the visible light region. By not allowing the result of Conditional Expression (6) to be equal to or greater than the upper limit, it becomes easy to ensure a difference in Abbe number between the negative lens and the positive lens, and it becomes easy to correct the primary chromatic aberration. In addition, in a case of a configuration in which Conditional Expression (6-1) is satisfied, it is possible to obtain more favorable characteristics. 50<νdn<65  (6) 52<νdn<60  (6-1)

Assuming that an average value of the refractive indices of all the negative lenses in the second optical system U2 at the d line is Ndn, it is preferable to satisfy Conditional Expression (7). By not allowing the result of Conditional Expression (7) to be equal to or less than the lower limit, occurrence of higher order spherical aberration can be suppressed, and a material with a small Abbe number can be easily selected. As a result, there is an advantage in correction of primary chromatic aberration. By not allowing the result of Conditional Expression (7) to be equal to or greater than the upper limit, the absolute value of the Petzval sum can be minimized, and the field curvature can be corrected well. In addition, in a case of a configuration in which Conditional Expression (7-1) is satisfied, it is possible to obtain more favorable characteristics. In a case of a configuration in which Conditional Expression (7-2) is satisfied, it is possible to obtain further more favorable characteristics. 1.5<Ndn<1.75  (7) 1.55<Ndn<1.7  (7-1) 1.57<Ndn<1.65  (7-2)

Assuming that an average value of the partial dispersion ratios of all the negative lenses in the second optical system between the g line and the F line U2 is θgFn, it is preferable to satisfy Conditional Expression (8). By not allowing the result of Conditional Expression (8) to be equal to or less than the lower limit, it becomes easy to ensure a difference in Abbe number between the negative lens and the positive lens, and it becomes easy to correct the primary chromatic aberration. By not allowing the result of Conditional Expression (8) to be equal to or greater than the upper limit, it becomes easy to correct the secondary chromatic aberration in the visible light region. In addition, in a case of a configuration in which Conditional Expression (8-1) is satisfied, it is possible to obtain more favorable characteristics. 0.53<θgFn<0.58  (8) 0.535<θgFn<0.565  (8-1)

Assuming that an average value of the partial dispersion ratios of all the positive lenses in the second optical system U2 between the g line and the F line is θgFp, it is preferable to satisfy Conditional Expression (9). By not allowing the result of Conditional Expression (9) to be equal to or less than the lower limit, it becomes easy to correct the secondary chromatic aberration in the visible light region. By not allowing the result of Conditional Expression (9) to be equal to or greater than the upper limit, it becomes easy to ensure a difference in Abbe number between the negative lens and the positive lens, and it becomes easy to correct the primary chromatic aberration. In addition, in a case of a configuration in which Conditional Expression (9-1) is satisfied, it is possible to obtain more favorable characteristics. 0.5<θgFp<0.65  (9) 0.52<θgFp<0.6  (9-1)

Assuming that an average value of the Abbe numbers of all the positive lenses in the second optical system U2 at the d line is νdp, it is preferable to satisfy Conditional Expression (10). By not allowing the result of Conditional Expression (10) to be equal to or less than the lower limit, it becomes easy to ensure a difference in Abbe number between the negative lens and the positive lens, and it becomes easy to correct the primary chromatic aberration. By not allowing the result of Conditional Expression (10) to be equal to or greater than the upper limit, it becomes easy to select a material having a large partial dispersion ratio between the g line and the F line, and it becomes easy to correct the secondary chromatic aberration in the visible light region. In addition, in a case of a configuration in which Conditional Expression (10-1) is satisfied, it is possible to obtain more favorable characteristics. 70<νdp<100  (10) 72<νdp<90  (10-1)

Assuming that an average value of the refractive indices of all the positive lenses in the second optical system U2 at the d line is Ndp, it is preferable to satisfy Conditional Expression (11). By not allowing the result of Conditional Expression (11) to be equal to or less than the lower limit, the absolute value of the Petzval's sum can be suppressed small while suppressing occurrence of spherical aberration, and field curvature can be corrected well. By not allowing the result of Conditional Expression (11) to be equal to or greater than the upper limit, it becomes easy to select a material having a large Abbe number. As a result, there is an advantage in correction of primary chromatic aberration. In addition, in a case of a configuration in which Conditional Expression (11-1) is satisfied, it is possible to obtain more favorable characteristics. 1.43<Ndp<1.75  (11) 1.44<Ndp<1.55  (11-1)

Assuming that a focal length of the second optical system U2 at the telephoto end is fU2 and a focal length of the first lens group G1 is fG1, it is preferable to satisfy Conditional Expression (12). By not allowing the result of Conditional Expression (12) to be equal to or less than the lower limit, it is possible to achieve a high variable magnification ratio even in a case where the amount of movement of the first lens group G1 during changing magnification is reduced. By not allowing the result of Conditional Expression (12) to be equal to or greater than the upper limit, fluctuation in spherical aberration during changing magnification can be suppressed. In addition, in a case of a configuration in which Conditional Expression (12-1) is satisfied, it is possible to obtain more favorable characteristics. 0.2<fU2/fG1<0.45  (12) 0.22<fU2/fG1<0.4  (12-1)

Assuming that a radius of curvature of the reflective surface of the first mirror is rM1 and a radius of curvature of the reflective surface of the second mirror is rM2, it is preferable to satisfy Conditional Expression (13). By not allowing the result of Conditional Expression (13) to be equal to or less than the lower limit, there is an advantage in shortening the total length. By not allowing the result of Conditional Expression (13) to be equal to or greater than the upper limit, it is possible to suppress occurrence of astigmatism. In addition, in a case of a configuration in which Conditional Expression (13-1) is satisfied, it is possible to obtain more favorable characteristics. In a case of a configuration in which Conditional Expression (13-2) is satisfied, it is possible to obtain further more favorable characteristics. 1<rM1/rM2<2.5  (13) 1.2<rM1/rM2<2.2  (13-1) 1.6<rM1/rM2<2.1  (13-2)

Assuming that a radius of curvature of the reflective surface of the first mirror is rM1 and a focal length of the correction lens group Gc is fC, it is preferable to satisfy Conditional Expression (14). By not allowing the result of Conditional Expression (14) to be equal to or less than the lower limit, there is an advantage in correction of spherical aberration. By not allowing the result of Conditional Expression (14) to be equal to or greater than the upper limit, longitudinal chromatic aberration can be suppressed and occurrence of difference in spherical aberration due to wavelength can be suppressed. In addition, in a case of a configuration in which Conditional Expression (14-1) is satisfied, it is possible to obtain more favorable characteristics. In a case of a configuration in which Conditional Expression (14-2) is satisfied, it is possible to obtain further more favorable characteristics. 0.07<rM1/fC<0.5  (14) 0.1<rM1/fC<0.45  (14-1) 0.2<rM1/fC<0.4  (14-2)

Assuming that a lateral magnification of the second optical system U2 at the telephoto end during focusing on an object at infinity is βrT and a variable magnification ratio of the variable magnification optical system is MAG, it is preferable to satisfy Conditional Expression (15). By not allowing the result of Conditional Expression (15) to be equal to or less than the lower limit, fluctuation in spherical aberration during changing magnification can be suppressed. By not allowing the result of Conditional Expression (15) to be equal to or greater than the upper limit, it is possible to achieve a high variable magnification ratio even in a case where the amount of movement of the lens group moving during changing magnification is reduced. In addition, in a case of a configuration in which Conditional Expression (15-1) is satisfied, it is possible to obtain more favorable characteristics. −0.45<βrT/MAG<−0.25  (15) −0.4<βrT/MAG<−0.28  (15-1)

Assuming that a focal length of the field lens group Gfd is fFd and a distance on the optical axis from the intermediate image, which is formed during focusing on the object at infinity, to the lens surface at the position closest to the object side in the second lens group G2 at the wide-angle end is LA, it is preferable to satisfy Conditional Expression (16). By satisfying Conditional Expression (16), it is possible to make the off-axis light intersect the optical axis Z at an appropriate position. As a result, there is an advantage in reducing the diameter of the lens group moving during changing magnification. In addition, in a case of a configuration in which Conditional Expression (16-1) is satisfied, it is possible to obtain more favorable characteristics. In a case of a configuration in which Conditional Expression (16-2) is satisfied, it is possible to obtain further more favorable characteristics. 0.4<fFd/LA<1  (16) 0.5<fFd/LA<0.8  (16-1) 0.55<fFd/LA<0.75  (16-2)

Assuming that a focal length of the first lens group G1 is fG1 and a focal length of the second lens group G2 is fG2, it is preferable to satisfy Conditional Expression (17). By satisfying Conditional Expression (17), it is possible to appropriately distribute the refractive power to the first lens group G1 and the second lens group G2. Thereby, it is possible to suppress fluctuation in spherical aberration during changing magnification, and it is also possible to reduce the effective diameters of the first lens group G1 and the second lens group G2. In addition, in a case of a configuration in which Conditional Expression (17-1) is satisfied, it is possible to obtain more favorable characteristics. 1.5<fG1/fG2<4  (17) 1.7<fG1/fG2<3.8  (17-1)

Although not shown in FIG. 1, various types of parallel plate shaped filters and/or cover glasses may be disposed between the lens closest to the image side and the image plane Sim and/or between an optical element and an optical element. It is possible to modify change in aberration, which is caused by arranging the various filters and/or the cover glass, to such a degree that does not cause a practical problem, by changing a small number of design parameters.

The above-mentioned preferred configurations and available configurations may be optional combinations, and it is preferable to selectively adopt the configurations in accordance with required specification. According to the present embodiment, it is possible to realize a variable magnification optical system, which has small fluctuations in various aberrations during changing magnification and has favorable optical performance while achieving a high variable magnification ratio. It should be noted that the “high variable magnification ratio” described herein means that the variable magnification ratio is equal to or greater than 4 times.

Next, numerical examples of the variable magnification optical system of the present invention will be described.

Example 1

A cross-sectional view and an optical path of a variable magnification optical system of Example 1 are shown in FIG. 1, and a configuration and an illustration method thereof is as described above. Therefore, repeated descriptions are partially omitted herein. The variable magnification optical system of Example 1 consists of, in order from the object side to the image side, a first optical system U1 and a second optical system U2. The first optical system U1 remains stationary with respect to an image plane Sim during changing magnification. The second optical system U2 includes a plurality of lens groups that move during changing magnification. The first optical system U1 consists of a ring-shaped first mirror M1, a second mirror M2, a correction lens group Gc, and a field lens group Gfd. The correction lens group Gc consists of one lens Lc1. The field lens group Gfd consists of two lenses Lf1 and Lf2 in order from the object side. The optical elements of the first optical system U1 all have a common optical axis Z. An intermediate image is formed in the vicinity of the object side of the field lens group Gfd in a state where the object at infinity is in focus. The first mirror M1 is an optical element having a power at the position closest to the object side in the optical path and also functions as a stop surface. Light from the object passes through the first mirror M1, the correction lens group Gc, the second mirror M2, the correction lens group Gc, and the field lens group Gfd in this order, and is then incident into the second optical system U2. The second optical system U2 consists of, in order from the object side, a first lens group G1 having a positive refractive power, a second lens group G2 having a positive refractive power, a third lens group G3 having a negative refractive power, and a fourth lens group G4 having a positive refractive power. During changing magnification, the first lens group G1, the second lens group G2, and the third lens group G3 move in the direction of the optical axis with loci different from one another, and the fourth lens group G4 remains stationary with respect to the image plane Sim. The first lens group G1 consists of three lenses L11 to L13. The second lens group G2 consists of one lens L21. The third lens group G3 consists of four lenses L31 to L34. The fourth lens group G4 consists of one lens L41. The third lens group G3 has a cemented lens in which a positive lens and a negative lens are cemented. The outline of the variable magnification optical system of Example 1 has been described above.

Table 1 shows basic lens data of the variable magnification optical system of Example 1, Table 2 shows specification and variable surface distances, and Table 3 shows aspheric surface coefficients thereof. Tables 1 and 2 show data in a state where the object at infinity is in focus. Table 1 shows constituent elements along the optical path. In Table 1, the column of the surface number shows surface numbers. The surface closest to the object side on the optical path is the first surface, and the surface numbers increase one by one toward the image side along the optical path. The column of r shows radii of curvature of the respective surfaces. The column of d shows surface distances on the optical axis between the respective surfaces and the surfaces adjacent to the image side on the optical path. The column of material shows the material names of the respective constituent elements and the names of the manufacturers of the materials with under bars interposed therebetween. The manufacturer names are shown schematically. For example, “OHARA” is OHARA CORPORATION. The column of Nd in Table 1 shows the refractive indices of the respective constituent elements at the d line. The column of νd shows the Abbe numbers of the respective constituent elements at the d line. The column of θgF shows the partial dispersion ratios of the respective constituent elements between the g line and the F line. The column of θCt shows the partial dispersion ratios of the respective constituent elements between the C line and the t line.

In Table 1, the sign of the radius of curvature of the surface convex toward the object side is positive and the sign of the radius of curvature of the surface convex toward the image side is negative. In the column of the surface number in Table 1, in addition to each surface number, “(reflective surface)” is attached to the surface corresponding to the reflective surface “(intermediate image)” is attached to the surface corresponding to the intermediate image, and “(image plane)” is attached to the surface corresponding to the image plane Sim. In Table 1, the variable surface distance is written in the column of d, where the surface number of the object side surface corresponding to the distance is attached to “D”.

In Table 2, the absolute value of the focal length of the whole system, the F number, the maximum image height, and the maximum half angle of view are shown in the rows labeled “|Focal length|”, “FNo.”, “Image height”, and “Half angle of view”, respectively. Table 2 shows the values of the variable surface distances. The values shown in Table 2 are values on the d line basis. In Table 2, the respective values of the wide-angle end state, the first intermediate focal length state, the second intermediate focal length state, and the telephoto end state are shown in the columns labeled W, M1, M2, and T, respectively.

In Table 1, the reference sign * is attached to surface numbers of aspheric surfaces, and numerical values of the paraxial radius of curvature are written into the column of the radius of curvature of the aspheric surface. Table 3 shows surface numbers of aspheric surfaces, and the rows of K and Am (m=4, 6, 8, 10) show numerical values of aspheric surface coefficients of the respective aspheric surfaces. The “E±n” (n: an integer) in numerical values of the aspheric surface coefficients of Table 3 indicates “×10^(±n)”. K and Am are the aspheric surface coefficients in the aspheric expression represented by the following expression. Zd=C×h ²/{1+(1−(1+K)×C ² ×h ²)^(1/2) }+ΣAm××h ^(m)

Here, Zd is an aspheric surface depth (a length of a perpendicular from a point on an aspheric surface at height h to a plane that is perpendicular to the optical axis and contacts with the vertex of the aspheric surface),

h is a height (a distance from the optical axis to the lens surface),

C is an inverse of a paraxial radius of curvature, and

K and Am are aspheric surface coefficients, and

Σ in the aspheric surface expression means the sum with respect to m.

In data of each table, a degree is used as a unit of an angle, and mm (millimeter) is used as a unit of a length, but appropriate different units may be used since the optical system can be used even in a case where the system is enlarged or reduced in proportion. Further, each of the following tables shows numerical values rounded off to predetermined decimal places.

TABLE 1 Example 1 Surface number r d Material Nd νd θgF θCt  1 (Reflective −1033.81950 −316.344 surface)  2* 135.65558 −35.000 LBSLOHARA 1.516330 64.06 0.5333 0.8785  3* 143.67806 −0.200  4 (Reflective −831.53073 0.200 surface)  5* 143.67806 35.000 LBSL7_OHARA 1.516330 64.06 0.5333 0.8785  6* 135.65558 0.000  7 (Intermediate ∞ 3.560 image)  8 −51.26904 14.405 SNBH56_OHARA 1.854780 24.80 0.6122 0.6739  9 71.05768 15.000 SLAH88_OHARA 1.916500 31.60 0.5911 0.7059 10 −48.49433 D10 11 −22.56452 3.200 SLAL59_OHARA 1.733997 51.47 0.5486 0.8067 12 66.03152 1.749 13 9397.11500 9.462 SFPL53_OHARA 1.438750 94.93 0.5340 0.8373 14 −31.43051 0.200 15 121.79684 13.350 SFPL53_OHARA 1.438750 94.93 0.5340 0.8373 16 −30.30142 D16 17 35.62791 11.146 SFPL53_OHARA 1.438750 94.93 0.5340 0.8373 18 −160.92832 D18 19 35.24937 3.300 SFPL53_OHARA 1.438750 94.93 0.5340 0.S373 20 50.73617 0.200 21 23.48294 7.272 SFPL53_OHARA 1.438750 94.93 0.5340 0.8373 22 −63.70289 2.178 SBAL41_OHARA 1.563839 60.67 0.5402 0.8370 23 16.23503 5.280 24 −37.39752 3.822 SBSL7_OHARA 1.516330 64.14 0.5353 0.8687 25 −90.13226 D25 26 2456.86976 2.800 SLAH55V_OHARA 1.834807 42.73 0.5648 0.7563 27 −171.39974 40.251 28 (Image plane) ∞

TABLE 2 Example 1 W M1 M2 T |Focal length| 500.007 1036.655 1399.998 2501.077 FNo. 3.125 6.479 8.750 15.632 Image height 8.000 8.000 8.000 8.000 Half angle of view 0.917 0.463 0.327 0.183 D10 135.264 70.000 49.821 32.910 D16 3.142 44.324 43.953 11.343 D18 2.075 2.300 2.431 2.641 D25 10.601 34.458 54.877 104.188

TABLE 3 Example 1 Second surface Sixth surface K   2.4308490E+00 A4 −2.3068712E−07 A6   1.3696765E−12 A8 −7.7228548E−15 A10   0.0000000E+00 Third surface Fifth surface K −1.5862915E+00 A4 −2.7678049E−08 A6   1.7465463E−11 A8 −5.7911503E−15 A10   0.0000000E+00

FIG. 11 shows aberration diagrams in a state where an object at the infinity is brought into focus through the variable magnification optical system of Example 1. In FIG. 11, in order from the left side, spherical aberration, astigmatism, distortion, and lateral chromatic aberration are shown. In FIG. 11, aberrations at the wide-angle end state are shown in the upper part indicated by WIDE, and aberrations at the telephoto end state are shown in the lower part indicated by TELE. In the spherical aberration diagram, the aberrations at a wavelength of 1970.1 nm, the C line, the d line, the F line, and the g line are indicated by the long dashed line, the chain line, the solid line, the short dashed line, and the chain double-dashed line, respectively. In the astigmatism diagram, aberration in the sagittal direction at the d line is indicated by the solid line, and aberration in the tangential direction at the d line is indicated by the short dashed line. In the distortion diagram, aberration at the d line is indicated by the solid line. In the lateral chromatic aberration diagram, the aberration at the wavelength of 1970.1 nm and the g line is indicated by the long dashed line and the chain double-dashed line, respectively. In the spherical aberration diagram, FNo. indicates the F number. In the other aberration diagrams, IH indicates the image height. Since the first mirror M1 has a ring shape, the data in the vicinity of 0 on the vertical axis of the spherical aberration diagram of FIG. 11 is shown as reference data.

Symbols, meanings, description methods, and illustration methods of the respective data pieces according to Example 1 are the same as those in the following examples unless otherwise noted. Therefore, in the following description, repeated description will be omitted.

Example 2

FIG. 2 shows a cross-sectional view and an optical path of the variable magnification optical system of Example 2. The variable magnification optical system of Example 2 has the same configuration as the outline of the variable magnification optical system of Example 1. Table 4 shows basic lens data of the variable magnification optical system of Example 2, Table 5 shows specification and variable surface distances, and FIG. 12 shows aberration diagrams thereof.

TABLE 4 Example 2 Surface number r d Material Nd νd θgF θCt  1 (Reflective −940.33887 −295.360 surface)  2 163.45951 −35.000 SFSL5_OHARA 1.487490 70.23 0.5300 0.8924  3 158.26945 −11.507  4 (Reflective −492.11463 11.507 surface)  5 158.26945 35.000 SFSL5_OHARA 1.487490 70.23 0.5300 0.8924  6 163.45951 295.560  7 (Intermediate ∞ 2.640 image)  8 −98.83269 14.797 SNBH56_OHARA 1.854780 24.80 0.6122 0.6739  9 186.03574 14.407 SLAH88_OHARA 1.916500 31.60 0.5911 0.7059 10 −63.52799 D10 11 −20.22194 3.200 SLAL59_OHARA 1.733997 51.47 0.5486 0.8067 12 70.08051 1.808 13 −677.79831 8.251 SFPL53_OHARA 1.438750 94.93 0.5340 0.8373 14 −28.43741 0.200 15 129.06346 11.928 SFPL53_OHARA 1.438750 94.93 0.5340 0.8373 16 −27.89917 D16 17 35.78594 13.782 SFPL53_OHARA 1.438750 94.93 0.5340 0.8373 18 235.02306 D18 19 40.31663 3.300 SFPL53_OHARA 1.438750 94.93 0.5340 0.8373 20 182.77982 0.200 21 21.85254 7.807 SFPL53_OHARA 1.438750 94.93 0.5340 0.8373 22 −54.44619 2.021 SBAL41_OHARA 1.563839 60.67 0.5402 0.8370 23 15.24145 6.357 24 −35.58368 2.000 SBSL7_OHARA 1.516330 64.14 0.5353 0.8687 25 −112.05865 D25 26 922.59801 4.036 SYGH51_OHARA 1.754999 52.32 0.5475 0.8107 27 −166.51349 40.150 28 (Image plane) ∞

TABLE 5 Example 2 W M1 M2 T |Focal length| 500.039 1224.572 1399.989 2497.541 FNo. 3.125 7.654 8.750 15.610 Image height 8.000 8.000 8.000 8.000 Half angle of 0.917 0.374 0.327 0.184 view D10 146.085 70.000 63.362 46.788 D16 3.746 42.125 39.876 5.033 D18 9.207 9.161 9.244 9.418 D25 2.009 39.762 48.566 99.809

Example 3

FIG. 3 shows a cross-sectional view and an optical path of the variable magnification optical system of Example 3. The variable magnification optical system of Example 3 is different from the variable magnification optical system of Example 1 in that the correction lens group Gc consists of two lenses Lc1 and Lc2 and the third lens group G3 consists of three lenses L31 to L33. The other configuration is the same as the outline of the variable magnification optical system of Example 1. Table 6 shows basic lens data of the variable magnification optical system of Example 3, Table 7 shows specification and variable surface distances, and FIG. 13 shows aberration diagrams thereof.

TABLE 6 Example 3 Surface number r d Material Nd νd θgF θCt  1 (Reflective −922.75595 −294.382 surface)  2 189.54097 −10.000 SFSLS_OHARA 1.487490 70.23 0.5300 0.8924  3 1188.04152 −17.474  4 775.56532 −10.000 SFSL5_OHARA 1.487490 70.23 0.5300 0.8924  5 168.65411 −0.200  6 (Reflective −483.32143 0.200 surface)  7 168.65411 10.000 SFSL5_OHARA 1.487490 70.23 0.5300 0.8924  8 775.56532 17.474  9 1188.04152 10.000 SFSL5_OHARA 1.487490 70.23 0.5300 0.8924 10 189.54097 294.619 11 (Intermediate ∞ 3.810 image) 12 −57.05882 14.856 SNBH56_OHARA 1.854780 24.80 0.6122 0.6739 13 848.85181 14.868 SLAH88_OHARA 1.916500 31.60 0.5911 0.7059 14 −50.50565 D14 15 −21.92011 3.200 SLAL59_OHARA 1.733997 51.47 0.5486 0.8067 16 70.08315 1.8457 17 −1000.87953 9.379 SFPL53_OHARA 1.438750 94.93 0.5340 0.8373 18 −29.90597 0.2000 19 117.46531 12.938 SFPL53_OHARA 1.438750 94.93 0.5340 0.8373 20 −30.24255 D20 21 41.54994 14.161 SFPL53_OHARA 1.438750 94.93 0.5340 0.8373 22 −211.60538 D22 23 27.74930 9.988 SFPL53_OHARA 1.438750 94.93 0.5340 0.8373 24 −55.08377 2.046 SBAL41_OHARA 1.563839 60.67 0.5402 0.8370 25 21.88803 6.468 26 −26.95242 2.000 SBSL7_OHARA 1.516330 64.14 0.5353 0.8687 27 −30.14825 D27 28 93.06881 2.000 SLAH55V_OHARA 1.834807 42.73 0.5648 0.7563 29 176.36037 52.182 30 (Image plane) ∞

TABLE 7 Example 3 W M1 M2 T |Focal length| 500.485 1117.112 1400.022 2475.451 FNo. 3.128 6.982 8.750 15.472 Image height 8.000 8.000 8.000 8.000 Half angle of 0.916 0.410 0.327 0.185 view D14 149.026 70.000 55.561 34.238 D20 3.545 49.642 49.123 18.792 D22 3.230 2.259 2.420 2.765 D27 2.000 35.900 50.696 102.006

Example 4

FIG. 4 shows a cross-sectional view and an optical path of the variable magnification optical system of Example 4. The variable magnification optical system of Example 4 is different from that of Example 1 in that the correction lens group Gc consists of two lenses Lc1 and Lc2. The other configuration is the same as the outline of the variable magnification optical system of Example 1. Table 8 shows basic lens data of the variable magnification optical system of Example 4, Table 9 shows specification and variable surface distances, and FIG. 14 shows aberration diagrams thereof.

TABLE 8 Example 4 Surface number r d Material Nd νd θgF θCt  1 (Reflective −953.77868 −286.986 surface)  2 232.21307 −10.000 SBSL7_OHARA 1.516330 64.14 0.5353 0.8687  3 390.17511 −32.789  4 300.32692 −10.000 SBSL7_OHARA 1.516330 64.14 0.5353 0.8687  5 184.88521 −0.200  6 (Reflective −508.96238 0.200 surface)  7 184.88521 10.000 SBSL7_OHARA 1.516330 64.14 0.5353 0.8687  8 300.32692 32.789  9 390.17511 10.000 SBSL7_OHARA 1.516330 64.14 0.5353 0.8687 10 232.21307 287.186 11 (Intermediate ∞ 3.939 image) 12 −53.49439 14.432 SNBH56_OHARA 1.854780 24.80 0.6122 0.6739 13 92.68066 15.000 SLAH88_OHARA 1.916500 31.60 0.5911 0.7059 14 −50.17468 D14 15 −23.57864 3.200 SLAL10_OHARA 1.719995 50.23 0.5521 0.7931 16 70.45288 2.0203 17 641.58789 9.923 SFPL53_OHARA 1.438750 94.93 0.5340 0.8373 18 −33.26453 0.8596 19 143.69669 15.000 CAF2_SCHOTT 1.433848 95.23 0.5386 0.8031 20 −32.97214 D20 21 35.50896 15.000 SFPL53_OHARA 1.438750 94.93 0.5340 0.8373 22 −178.58929 D22 23 33.09074 3.300 SFPL53_OHARA 1.438750 94.93 0.5340 0.8373 24 51.55537 0.200 25 21.89785 7.017 SFPL53_OHARA 1.438750 94.93 0.5340 0.8373 26 −61.72367 2.040 SBAL41_OHARA 1.563839 60.67 0.5402 0.8370 27 15.20944 5.086 28 −33.60080 9.237 SNSL36_OHARA 1.517417 52.43 0.5564 0.7992 29 −87.39336 D29 30 1302.49303 2.000 SLAH55V_OHARA 1.834807 42.73 0.5648 0.7563 31 −172.47891 40.000 32 (Image plane) ∞

TABLE 9 Example 4 W M1 M2 T |Focal length| 500.485 1117.112 1400.022 2475.451 FNo. 3.128 6.982 8.750 15.472 Image height 8.000 8.000 8.000 8.000 Half angle of view 0.916 0.410 0.327 0.185 D14 143.316 70.000 51.042 32.247 D20 3.000 51.755 53.198 24.447 D22 3.255 3.455 3.536 3.686 D29 2.000 26.362 43.795 91.192

Example 5

FIG. 5 shows a cross-sectional view and an optical path of the variable magnification optical system of Example 5. The variable magnification optical system of Example 5 is different from that of Example 1 in that the correction lens group Gc consists of two lenses Lc1 and Lc2. The other configuration is the same as the outline of the variable magnification optical system of Example 1. Table 10 shows basic lens data of the variable magnification optical system of Example 5, Table 11 shows specification and variable surface distances, and FIG. 15 shows aberration diagrams thereof.

TABLE 10 Example 5 Surface number r d Material Nd νd θgF θCt  1 (Reflective −946.65257 −284.821 surface)  2 219.86076 −10.000 SBSL7_OHARA 1.516330 64.14 0.5353 0.8687  3 343.36358 −30.232  4 267.59406 −10.000 SBSL7_OHARA 1.516330 64.14 0.5353 0.8687  5 176.67587 −0.200  6 (Reflective −522.63966 0.200 surface)  7 176.67587 10.000 SBSL7_OHARA 1.516330 64.14 0.5353 0.8687  8 267.59406 30.232  9 343.36358 10.000 SBSL7_OHARA 1.516330 64.14 0.5353 0.8687 10 219.86076 285.021 11 (Intermediate ∞ 3.640 image) 12 −56.16891 15.000 SNBH56_OHARA 1.854780 24.80 0.6122 0.6739 13 95.93933 15.000 SLAH88_OHARA 1.916500 31.60 0.5911 0.7059 14 −51.30080 D14 15 −22.22604 3.200 SLAL59_OHARA 1.733997 51.47 0.5486 0.8067 16 66.72028 1.7968 17 7888.01964 9.402 SFPL53_OHARA 1.438750 94.93 0.5340 0.8373 18 −31.19160 0.2000 19 122.59768 13.121 SFPL53_OHARA 1.438750 94.93 0.5340 0.8373 20 −30.25946 D20 21 36.27005 14.247 SFPL53_OHARA 1.438750 94.93 0.5340 0.8373 22 −160.25600 D22 23 37.19780 3.300 SFPL51_OHARA 1.496999 81.54 0.5375 0.8258 24 48.82912 0.200 25 22.62490 7.223 SFPL53_OHARA 1.438750 94.93 0.5340 0.8373 26 −58.10744 2.005 SBAL41_OHARA 1.563839 60.67 0.5402 0.8370 27 16.16206 5.302 28 −36.63689 2.771 SBSL7_OHARA 1.516330 64.14 0.5353 0.8687 29 −88.57416 D29 30 775.40717 10.251 SLAH55V_OHARA 1.834807 42.73 0.5648 0.7563 31 −200.50089 40.000 32 (Image plane) ∞

TABLE 11 Example 5 W M1 M2 T |Focal length| 500.011 1101.262 1400.002 2500.929 FNo. 3.125 6.883 8.750 15.631 Image height 8.000 8.000 8.000 8.000 Half angle of 0.917 0.416 0.327 0.183 view D14 147.066 70.000 55.793 36.779 D20 3.000 50.686 50.095 19.247 D22 2.593 2.709 2.767 2.888 D29 5.228 34.492 49.232 98.972

Example 6

FIG. 6 shows a cross-sectional view and an optical path of the variable magnification optical system of Example 6. The variable magnification optical system of Example 6 is different from that of Example 1 in that the correction lens group Gc consists of two lenses Lc1 and Lc2. The other configuration is the same as the outline of the variable magnification optical system of Example 1. Table 12 shows basic lens data of the variable magnification optical system of Example 6, Table 13 shows specification and variable surface distances, and FIG. 16 shows aberration diagrams thereof.

TABLE 12 Example 6 Surface number r d Material Nd νd θgF θCt  1 (Reflective −943.04827 −283.613 surface)  2 221.89858 −10.457 SFSL5_OHARA 1.487490 70.23 0.5300 0.8924  3 373.33420 −30.316  4 293.61480 −10.000 SFSL5_OHARA 1.487490 70.23 0.5300 0.8924  5 178.94372 −0.200  6 (Reflective −512.38205 0.200 surface)  7 178.94372 10.000 SFSL5_OHARA 1.487490 70.23 0.5300 0.8924  8 293.61480 30.316  9 373.33420 10.457 SFSL5_OHARA 1.487490 70.23 0.5300 0.8924 10 221.89858 283.813 11 (Intermediate ∞ 3.656 image) 12 −56.09328 15.000 SNBH56_OHARA 1.854780 24.80 0.6122 0.6739 13 89.59245 15.000 SLAH88_OHARA 1.916500 31.60 0.5911 0.7059 14 −51.40885 D14 15 −22.32153 3.200 SLAL59_OHARA 1.733997 51.47 0.5486 0.8067 16 67.23511 1.8292 17 −3378.12014 9.468 SFPL53_OHARA 1.438750 94.93 0.5340 0.8373 18 −31.29870 0.2000 19 128.13684 13.415 SFPL53_OHARA 1.438750 94.93 0.5340 0.8373 20 −30.29020 D20 21 36.66872 14.576 SFPL53_OHARA 1.438750 94.93 0.5340 0.8373 22 −169.96893 D22 23 33.82244 3.300 SFPL53_OHARA 1.438750 94.93 0.5340 0.8373 24 51.64878 0.200 25 23.78425 7.296 SFPL53_OHARA 1.438750 94.93 0.5340 0.8373 26 −58.52656 2.061 SBAL41_OHARA 1.563839 60.67 0.5402 0.8370 27 16.24485 5.146 28 −39.54787 6.627 SBSL7_OHARA 1.516330 64.14 0.5353 0.8687 29 −115.44233 D29 30 1023.41055 5.918 SLAH55V_OHARA 1.834807 42.73 0.5648 0.7563 31 −189.04456 40.616 32 (Image plane) ∞

TABLE 13 Example 6 W M1 M2 T |Focal length| 500.008 1090.519 1400.000 2500.939 FNo. 3.125 6.816 8.750 15.631 Image height 8.000 8.000 8.000 8.000 Half angle of view 0.917 0.420 0.327 0.183 D14 147.171 70.000 55.075 36.160 D20 3.000 51.337 50.925 19.982 D22 2.722 2.889 2.953 3.080 D29 4.813 33.480 48.752 98.484

Example 7

FIG. 7 shows a cross-sectional view and an optical path of the variable magnification optical system of Example 7. The variable magnification optical system of Example 7 is different from Example 1 in that the correction lens group Gc consists of two lenses Lc1 and Lc2 and the configuration of the second optical system U2 is different. The configuration of the first optical system U1 is the same as that of the outline of the variable magnification optical system of Example 1 except the correction lens group Gc. The second optical system U2 of Example 7 consists of, in order from the object side, a first lens group G1 having a positive refractive power, a second lens group G2 having a positive refractive power, and a third lens group G3 having a positive refractive power. During changing magnification, the first lens group G1 and the second lens group G2 move in the direction of the optical axis with loci different from each other, and the third lens group G3 remains stationary with respect to the image plane Sim. The first lens group G1 consists of three lenses L11 to L13. The second lens group G2 consists of five lenses L21 to L25. The third lens group G3 consists of one lens L31. The second lens group G2 has a cemented lens in which a positive lens and a negative lens are cemented. The outline of the variable magnification optical system of Example 7 has been described above.

Table 14 shows basic lens data of the variable magnification optical system of Example 7, Table 15 shows specification and variable surface distances, and FIG. 17 shows aberration diagrams thereof.

TABLE 14 Example 7 Surface number r d Material Nd νd θgF θCt  1 (Reflective −963.16574 −289.965 surface)  2 240.24636 −11.873 SBSL7_OHARA 1.516330 64.14 0.5353 0.8687  3 454.57715 −30.787  4 347.79332 −10.000 SBSL7_OHARA 1.516330 64.14 0.5353 0.8687  5 193.22724 −0.200  6 (Reflective −522.14291 0.200 surface)  7 193.22724 10.000 SBSL7_OHARA 1.516330 64.14 0.5353 0.8687  8 347.79332 30.787  9 454.57715 11.873 SBSL7_OHARA 1.516330 64.14 0.5353 0.8687 10 240.24636 290.165 11 (Intermediate ∞ 3.514 image) 12 −61.84350 15.000 SNBH56_OHARA 1.854780 24.80 0.6122 0.6739 13 91.06144 15.000 SLAH88_OHARA 1.916500 31.60 0.5911 0.7059 14 −54.18851 D14 15 −21.85440 3.200 SLAL59_OHARA 1.733997 51.47 0.5486 0.8067 16 71.08112 1.8456 17 −931.27576 9.500 SFPL53_OHARA 1.438750 94.93 0.5340 0.8373 18 −30.64420 0.2000 19 137.92622 13.470 SFPL53_OHARA 1.438750 94.93 0.5340 0.8373 20 −30.31283 D20 21 36.37200 14.792 SFPL53_OHARA 1.438750 94.93 0.5340 0.8373 22 −165.07536 3.086 23 34.21656 3.300 SFPL53_OHARA 1.438750 94.93 0.5340 0.8373 24 48.44728 0.200 25 23.46475 7.328 SFPL53_OHARA 1.438750 94.93 0.5340 0.8373 26 −55.90379 2.000 SBAL41_OHARA 1.563839 60.67 0.5402 0.8370 27 16.34518 5.392 28 −36.92965 7.147 SBSL7_OHARA 1.516330 64.14 0.5353 0.8687 29 −87.59304 D29 30 179.02404 2.710 SLAH55V_OHARA 1.834807 42.73 0.5648 0.7563 31 22898.94031 40.002 32 (Image plane) ∞

TABLE 15 Example 7 W M1 M2 T |Focal length| 500.009 1122.717 1400.005 2500.933 FNo. 3.125 7.017 8.750 15.631 Image height 8.000 8.000 8.000 8.000 Half angle of 0.917 0.408 0.327 0.183 view D14 151.547 70.000 56.640 37.130 D20 3.000 54.406 54.138 24.040 D29 7.603 37.744 51.372 100.980

Example 8

FIG. 8 shows a cross-sectional view and an optical path of the variable magnification optical system of Example 8. The variable magnification optical system of Example 8 has the same configuration as the outline of the variable magnification optical system of Example 7. Table 16 shows basic lens data of the variable magnification optical system of Example 8, Table 17 shows specification and variable surface distances, and FIG. 18 shows aberration diagrams thereof.

TABLE 16 Example 8 Surface number r d Material Nd νd θgF θCt  1 (Reflective −938.69970 −281.849 surface)  2 249.10440 −12.737 SBSL7_OHARA 1.516330 64.14 0.5353 0.8687  3 513.03789 −32.370  4 388.76526 −10.000 SBSL7_OHARA 1.516330 64.14 0.5353 0.8687  5 197.90988 −0.200  6 (Reflective −488.98699 0.200 surface)  7 197.90988 10.000 SBSL7_OHARA 1.516330 64.14 0.5353 0.8687  8 388.76526 32.370  9 513.03789 12.737 SBSL7_OHARA 1.516330 64.14 0.5353 0.8687 10 249.10440 282.049 11 (Intermediate ∞ 3.628 image) 12 −58.89509 15.000 SNBH56_OHARA 1.854780 24.80 0.6122 0.6739 13 78.42668 15.000 SLAH88_OHARA 1.916500 31.60 0.5911 0.7059 14 −52.77514 D14 15 −22.69003 3.200 SLAL10_OHARA 1.719995 50.23 0.5521 0.7931 16 86.53277 2.1039 17 −2513.71582 10.059 SFPL53_OHARA 1.438750 94.93 0.5340 0.8373 18 −31.86847 0.8661 19 173.90341 15.000 CAF2_SCHOTT 1.433848 95.23 0.5386 0.8031 20 −33.73926 D20 21 34.09354 14.840 SFPL53_OHARA 1.438750 94.93 0.5340 0.8373 22 −176.01416 3.791 23 33.21222 3.012 SFPL53_OHARA 1.438750 94.93 0.5340 0.8373 24 51.22226 0.200 25 22.21014 7.081 SFPL53_OHARA 1.438750 94.93 0.5340 0.8373 26 −51.07424 2.000 SBAL41_OHARA 1.563839 60.67 0.5402 0.8370 27 15.32906 5.242 28 −31.32340 10.263 SNSL36_OHARA 1.516330 64.14 0.5353 0.8687 29 −72.51517 D29 30 142.64101 2.000 SLAH55V_OHARA 1.834807 42.73 0.5648 0.7563 31 745.52557 40.069 32 (Image plane) ∞

TABLE 17 Example 8 W M1 M2 T |Focal length| 500.010 1026.176 1400.005 2500.864 FNo. 3.125 6.414 8.750 15.630 Image height 8.000 8.000 8.000 8.000 Half angle of 0.917 0.447 0.327 0.183 view D14 144.290 70.000 50.698 32.468 D20 3.000 52.603 54.169 24.721 D29 2.000 26.687 44.423 92.100

Example 9

FIG. 9 shows a cross-sectional view and an optical path of the variable magnification optical system of Example 9. The variable magnification optical system of Example 9 is different from that of Example 7 in that the first lens group G1, the second lens group G2, and the third lens group G3 move in the direction of the optical axis with loci different from one another during changing magnification. The other configuration is the same as the outline of the variable magnification optical system of Example 7. Table 18 shows basic lens data of the variable magnification optical system of Example 9, Table 19 shows specification and variable surface distances, and FIG. 19 shows aberration diagrams thereof.

TABLE 18 Example 9 Surface number r d Material Nd νd θgF θCt  1 (Reflective −977.09951 −294.679 surface)  2 229.88146 −10.000 SBSL7_OHARA 1.516330 64.14 0.5353 0.8687  3 395.80136 −29.887  4 299.58796 −10.000 SBSL7_OHARA 1.516330 64.14 0.5353 0.8687  5 184.83788 −0.200  6 (Reflective −551.79666 0.200 surface)  7 184.83788 10.000 SBSL7_OHARA 1.516330 64.14 0.5353 0.8687  8 299.58796 29.887  9 395.80136 10.000 SBSL7_OHARA 1.516330 64.14 0.5353 0.8687 10 229.88146 294.879 11 (Intermediate ∞ 3.363 image) 12 −65.16245 14.948 SNBH56_OHARA 1.854780 24.80 0.6122 0.6739 13 62.75642 14.754 SLAH88_OHARA 1.916500 31.60 0.5911 0.7059 14 −55.41523 D14 15 −21.03798 3.200 SLAL59_OHARA 1.733997 51.47 0.5486 0.8067 16 72.36001 1.7582 17 −1272.75293 9.425 SFPL53_OHARA 1.438750 94.93 0.5340 0.8373 18 −30.35569 0.2000 19 151.22337 13.425 SFPL53_OHARA 1.438750 94.93 0.5340 0.8373 20 −29.69505 D20 21 35.82341 12.530 SFPL53_OHARA 1.438750 94.93 0.5340 0.8373 22 −169.82249 1.277 23 35.95511 5.250 SFPL53_OHARA 1.438750 94.93 0.5340 0.8373 24 54.29948 0.371 25 23.37249 7.265 SFPL53_OHARA 1.438750 94.93 0.5340 0.8373 26 −57.78747 2.000 SBAL41_OHARA 1.563839 60.67 0.5402 0.8370 27 15.91395 5.262 28 −35.23451 5.463 SBSL7_OHARA 1.516330 64.14 0.5353 0.8687 29 −80.75072 D29 30 119.88367 2.052 SLAL7_OHARA 1.651597 58.55 0.8270 0.5425 31 −7647.27929 D31 32 (Image plane) ∞

TABLE 19 Example 9 W M1 M2 T |Focal length| 500.010 1026.176 1400.005 2500.864 FNo. 3.125 6.414 8.750 15.630 Image height 8.000 8.000 8.000 8.000 Half angle of 0.917 0.442 0.327 0.183 view D14 141.509 70.000 52.163 31.923 D20 3.000 47.322 47.123 15.726 D29 7.77955 34.969 51.472 82.529 D31 40.203 40.200 41.732 62.314

Example 10

FIG. 9 shows a cross-sectional view and an optical path of the variable magnification optical system of Example 10. The variable magnification optical system of Example 10 is different from that of Example 7 in the configuration of the second optical system U2. The configuration of the first optical system U1 is the same as the outline of the variable magnification optical system of Example 7. The second optical system U2 of Example 10 consists of, in order from the object side, a first lens group G1 having a positive refractive power and a second lens group G2 having a positive refractive power. The first lens group G1 and the second lens group G2 move in the direction of the optical axis with loci different from one another during changing magnification. The first lens group G1 consists of three lenses L11 to L13. The second lens group G2 consists of seven lenses L21 to L27. The second lens group G2 has two sets of cemented lenses in which a positive lens and a negative lens are cemented. Table 20 shows basic lens data of the variable magnification optical system of Example 10, Table 21 shows specification and variable surface distances, Table 22 shows aspheric surface coefficients, and FIG. 20 shows aberration diagrams.

TABLE 20 Example 10 Surface number r d Material Nd νd θgF θCt  1 (Reflective −1009.60656 −306.892 surface)  2 155.49173 −20.000 SFSL5_OHARA 1.487490 70.23 0.5300 0.8924  3 152.20738 −8.000  4 224.52261 −16.331 SFSL5_OHARA 1.487490 70.23 0.5300 0.8924  5 226.68843 −0.200  6 (Reflective −646.86833 0.200 surface)  7 226.68843 16.331 SFSL5_OHARA 1.487490 70.23 0.5300 0.8924  8 224.52261 8.000  9 152.20738 20.000 SFSL5_OHARA 1.487490 70.23 0.5300 0.8924 10 155.49173 307.091 11 (Intermediate ∞ 4.754 image) 12 −43.05480 14.676 SNPH1W_OHARA 1.808095 22.76 0.6596 0.6307 13 99.29659 10.864 SLAH58_OHARA 1.882997 40.76 0.7397 0.5667 14 −44.27169 D14 15 −19.41182 3.200 SLAL8_OHARA 1.712995 53.87 0.5459 0.8194 16 −66.73802 1.6399 17 −62.57013 10.110 SFPL55_OHARA 1.438750 94.93 0.5340 0.8373 18* −23.97544 0.2028 19 −777.75180 9.888 CAF2_SCHOTT 1.433848 95.23 0.5386 0.8031 20 −41.30828 D20 21 34.95049 8.304 SFPL55_OHARA 1.438750 94.66 0.5340 0.8410 22 −87.47002 0.201 23 43.40566 2.372 SFPL55_OHARA 1.438750 94.66 0.5340 0.8410 24 45.07363 0.200 25 22.46084 7.466 SFPL55_OHARA 1.438750 94.66 0.5340 0.8410 26 −56.33990 2.037 SBSL7_OHARA 1.516330 64.14 0.5353 0.8687 27 16.19715 5.218 28 −24.80997 2.029 SLAM54_OHARA 1.756998 47.82 0.5565 0.7915 29 −44.63804 7.619 30 −77.80794 2.000 SNBH53V_OHARA 1.738000 32.33 0.5900 0.7154 31 251.64674 4.665 SBSM25_OHARA 1.658441 50.88 0.5560 0.7765 32 −36.09746 D32 33 (Image plane) ∞

TABLE 21 Example 10 W M1 M2 T |Focal length| 500.083 961.761 1399.980 2501.897 FNo. 3.126 6.011 8.750 15.637 Image height 8.000 8.000 8.000 8.000 Half angle of 0.917 0.442 0.327 0.183 view D14 143.435 70.000 39.601 15.286 D20 3.000 60.147 72.235 55.006 D32 42.67555 58.963 77.274 118.818

TABLE 22 Example 10 Eighteenth surface K −2.1807711E+00 A4 −1.8103223E−05 A6 2.7299174E−09 A8 −1.0242453E−11 A10 −1.4740880E−14

Table 23 shows values corresponding to Conditional Expressions (1) to (17) of the variable magnification optical systems of Examples 1 to 10. Corresponding values other than the partial dispersion ratios in Table 23 are values on the d line basis.

TABLE 23 Expression number Example 1 Example 2 Example 3 Example 4 Example 5 (1) θgFp − θgFn −0.0022 −0.0051 0.0073 −0.0097 −0.0017 (2) νdp − νdn 27.47 29.07 16.92 31.84 25.24 (3) θCtp − θCtn −0.0137 −0.0046 −0.0356 0.0083 −0.0156 (4) θCtn 0.8375 0.8375 0.8375 0.8098 0.8375 (5) θCtp 0.8238 0.8329 0.8019 0.8181 0.8219 (6) νdn 58.76 58.76 58.76 54.44 58.76 (7) Ndn 1.60472 1.60472 1.60472 1.60042 1.60472 (8) θgFn 0.5414 0.5414 0.5414 0.5496 0.5414 (9) θgFp 0.5391 0.5363 0.5487 0.5399 0.5397 (10) νdp 86.23 87.83 75.68 86.28 84.00 (11) Ndp 1.50476 1.49146 1.58438 1.50394 1.51447 (12) fU2/fG1 0.355 0.369 0.375 0.325 0.355 (13) rM1/rM2 1.243 1.911 1.909 1.874 1.811 (14) rM1/fC 0.107 0.293 0.264 0.275 0.252 (15) βrT/MAG −0.344 −0.346 −0.317 −0.319 −0.326 (16) fFd/LA 0.629 0.603 0.622 0.634 0.623 (17) fG1/fG2 3.539 2.643 2.617 3.760 3.561 Expression number Example 6 Example 7 Example 8 Example 9 Example 10 (1) θgFp − θgFn −0.0022 −0.0022 −0.0026 0.0415 −0.0185 (2) νdp − νdn 20.60 20.60 27.93 30.11 32.23 (3) θCtp − θCtn −0.0137 −0.0137 −0.0148 −0.0493 0.0315 (4) θCtn 0.8375 0.8375 0.8329 0.8375 0.7919 (5) θCtp 0.8238 0.8238 0.8181 0.7882 0.8233 (6) νdn 58.76 58.76 58.35 58.76 55.28 (7) Ndn 1.60472 1.60472 1.60005 1.60472 1.68108 (8) θgFn 0.5414 0.5414 0.5425 0.5414 0.5569 (9) θgFp 0.5391 0.5391 0.5399 0.5828 0.5384 (10) νdp 79.36 79.36 86.28 88.87 87.50 (11) Ndp 1.45168 1.45168 1.50394 1.47422 1.68108 (12) fU2/fG1 0.346 0.316 0.277 0.238 0.319 (13) rM1/rM2 1.841 1.845 1.920 1.771 1.561 (14) rM1/fC 0.269 0.284 0.377 0.238 0.232 (15) βrT/MAG −0.325 −0.325 −0.322 −0.329 −0.336 (16) fFd/LA 0.623 0.619 0.618 0.625 0.694 (17) fG1/fG2 3.602 1.953 2.289 2.328 1.855

As can be seen from the above data, in the variable magnification optical systems of Examples 1 to 10, fluctuation in various aberrations during changing magnification is small, the variable magnification ratio is equal to or greater than 4.9 times, a high variable magnification ratio is achieved, and the load of the object side portion can be reduced. In addition, the variable magnification optical system can be configured with low costs, various aberrations are satisfactorily corrected in a wide range from the visible light region to the infrared light region, and high optical performance is achieved.

Next, an imaging apparatus according to an embodiment of the present invention will be described. FIG. 21 is a schematic configuration diagram of an imaging apparatus 10 using the variable magnification optical system 1 according to the above-mentioned embodiment of the present invention as an example of an imaging apparatus of an embodiment of the present invention. As the imaging apparatus 10, for example, there is a surveillance camera, a video camera, an electronic still camera, or the like.

The imaging apparatus 10 comprises: the variable magnification optical system 1; a filter 4 that is disposed on the image side of the variable magnification optical system 1; an imaging element 5 that captures an image of a subject formed by the variable magnification optical system 1; a signal processing section 6 that arithmetically processes an output signal which is output from the imaging element 5; and a changing magnification controller 7 that changes the variable magnification ratio of the variable magnification optical system 1. FIG. 21 schematically shows the first optical system U1 and the second optical system U2 included in the variable magnification optical system 1. The imaging element 5 captures an image of a subject formed by the variable magnification optical system 1 and converts the image into an electric signal. The imaging element 5 is disposed such that the imaging surface thereof is coplanar with the image plane of the variable magnification optical system 1. As the imaging element 5, for example, it is possible to use a charge coupled device (CCD), a complementary metal oxide semiconductor (CMOS), or the like. It should be noted that FIG. 21 shows only one imaging element 5, but the imaging apparatus of the present invention is not limited to this, and may be a so-called three-plate imaging apparatus having three imaging elements.

The present invention has been hitherto described through embodiments and examples, but the present invention is not limited to the above-mentioned embodiments and examples, and may be modified into various forms. For example, values such as the radius of curvature, the surface distance, the refractive index, the Abbe number, and the aspheric surface coefficient of each optical element are not limited to the values shown in the numerical examples, and different values may be used therefor. 

What is claimed is:
 1. A variable magnification optical system consisting of, in order from an object side: a first optical system that includes two reflecting mirrors having reflective surfaces arranged to face each other and remains stationary with respect to an image plane during changing magnification; and a second optical system that includes at least two positive lenses and at least one negative lens, wherein the two reflecting mirrors consist of a first reflecting mirror that has a reflective surface concave toward the object side and reflects light, which is originated from an object, toward the object side, and a second reflecting mirror that has a reflective surface convex toward an image side and reflects the reflected light, which is reflected from the first reflecting mirror, toward the image side, wherein the second optical system includes, successively in order from a position closest to the object side, a first lens group that consistently moves to the object side during changing magnification from a wide-angle end to a telephoto end and has a positive refractive power, and a second lens group that moves in a direction of an optical axis with a locus different from a locus of the first lens group during changing magnification and has a positive refractive power, wherein an intermediate image is formed between the second reflecting mirror and the first lens group, and the intermediate image is re-formed through the second optical system, and wherein assuming that an average value of partial dispersion ratios of all the positive lenses in the second optical system between a g line and an F line is θgFp, and an average value of partial dispersion ratios of all the negative lenses in the second optical system between the g line and the F line is θgFn, Conditional Expression (1) is satisfied, −0.04<θgFp−θgFn<0.1  (1).
 2. The variable magnification optical system according to claim 1, wherein assuming that an average value of Abbe numbers of all the positive lenses in the second optical system at a d line is νdp, and an average value of Abbe numbers of all the negative lenses in the second optical system at the d line is νdn, Conditional Expression (2) is satisfied, 10<νdp−νdn<40  (2).
 3. The variable magnification optical system according to claim 1, wherein assuming that an average value of partial dispersion ratios of all the positive lenses in the second optical system between a C line and a t line is θCtp, and an average value of the partial dispersion ratios of all the negative lenses in the second optical system between the C line and the t line is θCtn, Conditional Expression (3) is satisfied, −0.1<θCtp−θCtn<0.1  (3).
 4. The variable magnification optical system according to claim 1, wherein the first optical system includes a field lens group that consists of two or less lenses and that has a positive refractive power and that is a lens component closest to the intermediate image.
 5. The variable magnification optical system according to claim 1, wherein the first reflecting mirror is an optical element having a power at a position closest to the object side on an optical path.
 6. The variable magnification optical system according to claim 1, wherein the first optical system includes a correction lens group consisting of two or less lenses which are disposed in an optical path from the first reflecting mirror to the second reflecting mirror and in an optical path from the second reflecting mirror to a position of the intermediate image and which have a common optical axis with respect to the first reflecting mirror and the second reflecting mirror.
 7. The variable magnification optical system according to claim 1, wherein assuming that an average value of the partial dispersion ratios of all the negative lenses in the second optical system between a C line and a t line is θCtn, Conditional Expression (4) is satisfied, 0.75<θCtn<0.9  (4).
 8. The variable magnification optical system according to claim 1, wherein assuming that an average value of the partial dispersion ratios of all the positive lenses in the second optical system between the C line and the t line is θCtp, Conditional Expression (5) is satisfied, 0.75<θCtp<0.9  (5).
 9. The variable magnification optical system according to claim 1, wherein assuming that an average value of Abbe numbers of all the negative lenses in the second optical system at a d line is νdn, Conditional Expression (6) is satisfied, 50<νdn<65  (6).
 10. The variable magnification optical system according to claim 1, wherein assuming that an average value of refractive indices of all the negative lenses in the second optical system at a d line is Ndn, Conditional Expression (7) is satisfied, 1.5<Ndn<1.75  (7).
 11. The variable magnification optical system according to claim 1, wherein Conditional Expression (8) is satisfied, 0.53<θgFn<0.58  (8).
 12. The variable magnification optical system according to claim 1, wherein Conditional Expression (9) is satisfied, 0.5<θgFp<0.65  (9).
 13. The variable magnification optical system according to claim 1, wherein assuming that an average value of Abbe numbers of all the positive lenses in the second optical system at a d line is νdp, Conditional Expression (10) is satisfied, 70<νdp<100  (10).
 14. The variable magnification optical system according to claim 1, wherein assuming that an average value of refractive indices of all the positive lenses in the second optical system at a d line is Ndp, Conditional Expression (11) is satisfied, 1.43<Ndp<1.75  (11).
 15. The variable magnification optical system according to claim 1, wherein Conditional Expression (1-1) is satisfied, −0.02<θgFp−θgFn<0.06  (1-1).
 16. The variable magnification optical system according to claim 2, wherein Conditional Expression (2-1) is satisfied, 14<νdp−νdn<35  (2-1).
 17. The variable magnification optical system according to claim 3, wherein Conditional Expression (3-1) is satisfied, −0.07<θCtp−θCtn<0.05  (3-1).
 18. The variable magnification optical system according to claim 7, wherein Conditional Expression (4-1) is satisfied, 0.77<θCtn<0.85  (4-1).
 19. The variable magnification optical system according to claim 8, wherein Conditional Expression (5-1) is satisfied, 0.78<θCtp<0.85  (5-1).
 20. An imaging apparatus comprising the variable magnification optical system according to claim
 1. 